Support for world time clock (i.e. any timezone)

[justinmassiot]

There are at least two ways to implement this:

1. Offset the Arduino clock with the user's timezone
2. Manage all times in UTC (GMT), i.e. with zero offset

Option 1 seems simpler and more straightforward, at least because:

• the current time would be readable in local time, making things easier to debug
• the stored times (agenda) would be in local time
• the couple [wake-up, sleep] times would be within the same day (not spread among two different days)
• the wake-up time should always be "lower" (i.e. triggered before) the sleep time, except in rare cases where the user purposely wants to live at night...

Option 2 may be better for portability, and would make debugging of other's device configuration simpler.

[justinmassiot]

Can the device also automatically get its timezone based on location from NTP?
This would be great because moving the device to an other location would automatically adjust its local time while still following the saved agenda!

[justinmassiot]

https://docs.arduino.cc/libraries/timezone/

Should we keep the RTC in UTC and implement getters and setters taking care of the timezone and DST offsets?

About the RTC time drift: https://forum.arduino.cc/t/arduino-rtc-does-not-stay-in-sync-despite-use-of-arduinocloud-getlocaltime/